clayfigThe dice are full-sized 16mm.
They are Synthetic Opalite, and hand carved. The density is consistent, but as they are hand-carved- it is impossible for stone dice to be perfect. Having that said, our customers have been impressed with the quality of carving on our stone dice. They produce random rolls within the normal tolerable range.
clayfigThere is no such thing as natural opalite. You are thinking of natural opals. Opalite (by definition synthetic) is a type of glass that is artificially made iridescent.
Google "opalite" or look it up on wikipedia to check what I just said above.